JP2005343755A - Method for solidifying cement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which is capable of solidifying easily and inexpensively cement even if the mixture thereof contains a borate. <P>SOLUTION: The method for solidifying cement, comprising hardening and solidifying a mixture 11, which contains at least a borate, boric acid or a nitrate, with cement 12, is characterized by forming a blend 15 by adding a film-forming agent 14 along with the mixture 11, cement 12 and water 13, and by forming a protective film 24, which is a compound of the film-forming agent 14 and a calcium component, around cement particles 22 earlier than the time of forming a film of a compound of the borate, the boric acid or the nitrate and the calcium component around the cement particles 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of solidifying a mixture containing borate such as boric acid waste using cement.

Low-level radioactive waste is emitted from nuclear power plants, nuclear fuel reprocessing facilities, or nuclear research facilities. This low-level radioactive waste is usually mixed with cement to cause a hydration reaction and solidified, and then stored in a predetermined storage facility. Cement is used for the solidification of the residue because it is inexpensive, can be solidified at room temperature, and a compressive strength that satisfies the legal standard value for soil storage of radioactive waste (1.5 N / mm ² ) is obtained. .

  Here, the residue contains borate, which is known to be incompatible with cement. That is, as shown in FIG. 9, when a cement 94, a borate 92, and water 93 are mixed to cause a hydration reaction to produce a cement solid 95, a hydration reaction occurs. As shown in FIG. 10, a coating 102 of calcium borate (or calcium silicate hydrate or calcium hydroxide), which is a compound of borate and calcium components, is formed around the cement particles 101. . As a result, there is a problem that the hydration reaction is less likely to occur in the cement particles 101, and it takes a long time for setting or insufficient strength.

  Therefore, as shown in FIG. 11, a hardening stimulant (sodium hydroxide aqueous solution or the like) 112 is added to the borate 111 to first form borax 113, and cement 114 and water 115 are mixed into the borax 113. There has been proposed a method of producing a cement solidified body 117 by causing a hydration reaction in the blend 116 (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-197690

  By the way, in order to solidify a large amount of borate 111 into cement, a large amount of aqueous sodium hydroxide solution (curing stimulant 112) is required. However, in this case, the number of steps is increased and a large amount of aqueous sodium hydroxide solution is used, so that the processing cost of the cement solidified body 117 is increased. Moreover, since the sodium hydroxide aqueous solution itself is a strong alkaline solution, there is a problem that handling is not good and it is difficult to manage the solution.

  The object of the present invention, which was created in view of the above circumstances, is to provide a method capable of solidifying cement easily and inexpensively even for a mixture containing borate.

  To achieve the above object, the cement solidification method according to the present invention is a method of solidifying a mixture containing at least borate, boric acid, or nitrate with cement, together with the mixture, cement, and water, A film former is formed around the cement particles faster than a compound film of borate, boric acid, or nitrate and calcium components is formed around the cement particles by adding a film former to form a blend. And forming a protective film which is a compound of calcium component.

  Here, it is preferable to add the film forming agent at a ratio of less than 20 wt% with respect to the cement. Moreover, it is preferable that a film formation agent is a low alkali type liquid quick-setting agent. Furthermore, it is preferable that the low alkali type liquid accelerator is an aqueous solution mainly composed of a water-soluble aluminum salt.

  On the other hand, the cement solidification method according to the present invention is a method in which a mixture containing at least borate, boric acid, or nitrate is solidified by cement and solidifies with the mixture, cement, and water. Is added to form a blend, which eliminates the fluidity of the blend faster than the formation of a borate, boric acid, or nitrate and calcium component coating around the cement particles. .

  Here, it is preferable to add the fluidity-reducing agent at a ratio of less than 20 wt% with respect to the cement. Moreover, it is preferable that a fluidity | liquidity loss agent is gypsum.

  On the other hand, the cement solidified body according to the present invention is solidified by using any of the above-described cement solidifying methods.

  According to this invention, the outstanding effect that the mixture containing at least borate, boric acid, or nitrate can be hardened and solidified with cement is exhibited.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a flow of a cement solidification method according to a preferred embodiment of the present invention.

  As shown in FIG. 1, in the cement solidification method according to the present embodiment, first, a film forming agent 14 is added together with a mixture 11 containing at least a borate (or boric acid or nitrate), cement 12, and water 13. Add to form formulation 15. The film forming agent 14 is preferably added to the cement 12 at a ratio of less than 20 wt%, preferably 1 to 15 wt%.

  Thereafter, in the formulation 15, the initial setting (a state in which fluidity is almost lost) occurs. At this time, as shown in FIG. 2, a coating of calcium borate (or a coating of calcium nitrate; see FIG. 10) around the cement particles 22 is a compound of a borate ion (or nitrate ion) 23 and a calcium component. The protective coating 24, which is a compound of the film forming agent 14 and the calcium component, is formed around the cement particles 22 earlier than the formation. “Condensation” is from the start to the end described later.

  Thereafter, the condensation proceeds, and finally the condensation is finished (a state in which the fluidity is almost lost). Thereby, the cement solidified body 16 is obtained. Thereafter, in the cement solid body 16, the hydration reaction of the cement gradually proceeds, and the hardening of the cement solid body 16 gradually proceeds. The cement hydration reaction proceeds for about 4 weeks from the beginning of setting, and after about 4 weeks, the hardening of the cement is completely (or almost completely) and a hardened body (not shown) is obtained. The strength of the cement solid body 16 is an apparent strength, and the strength of the cured body after the completion of curing is a true strength.

Here, as the mixture 11 containing at least borate, boric acid or nitrate, borate alone, boric acid alone, nitrate alone, or a mixture thereof (for example, a mixture of nitrate and borate) Etc.). Examples of the mixture of nitrate and borate include a mixture of sodium nitrate (NaNO ₃ ) and sodium tetraborate (Na ₂ B ₄ O ₇ ) at a weight ratio of 2: 1.

  Further, the film forming agent 14 is preferably a low alkali, and examples thereof include a low alkali type liquid quick setting agent. The low alkali type liquid quick setting agent is not particularly limited, and any of those conventionally used as a quick setting agent for sprayed concrete can be applied. Specifically, an aqueous solution containing a water-soluble aluminum salt as a main component, preferably an aqueous solution containing a water-soluble aluminum salt containing a sulfate as a main component, more preferably a composite such as a sulfate, fluoride salt or oxalate. An aqueous solution containing a water-soluble aluminum salt containing as a main component. As such an aqueous solution, for example, Meiko SA163 (registered trademark, manufactured by NMB Co., Ltd.) can be mentioned.

  The addition ratio of the film forming agent 14 to the cement 12 is less than 20 wt% in weight ratio. If the addition ratio is more than 20 wt%, the condensation progresses instantaneously and cannot be uniformly solidified, resulting in an increase in cost. Because.

  The ratio of borate (or nitrate) contained in the mixture 11 to the cement 12 is preferably less than 70 wt% by weight. Here, when the ratio of the borate (or nitrate) to the cement 12 exceeds 70 wt%, the cement 12 cannot be sufficiently solidified because the ratio of the cement 12 is too small.

  Next, the operation of the present embodiment will be described.

  When a water-soluble aluminum salt is used as the film-forming agent 14, a protective film 24 of aluminate hydrate is formed around the cement particles 22 after the mixing until the start of setting. The production rate (reaction rate) of the aluminate hydrate protective coating 24 is faster than the production rate (reaction rate) of the calcium borate coating (or calcium nitrate coating). Therefore, as shown in FIG. 2, the protective coating 24 prevents contact between the cement particles 22 and the borate ions (or nitrate ions) 23. As a result, a calcium borate coating (or calcium nitrate coating) is not generated around the cement particles 22, and the hydration reaction of the cement particles 22 is not likely to be inhibited.

In addition, a protective coating 24 such as aluminate hydrate generated around the cement particles 22 reacts with the cement particles 22, whereby various hydrates (calcium aluminate hydrate, ettringite; Ca ₆ Al ₂ (SO ₄ ) ₃ (OH) ₂ .26H ₂ O]. The formation of these hydrates promotes the hydration reaction of the cement. As a result, as compared with the case where the film forming agent 14 is not added, the hardening of the cement is completed in a short time, and the true strength of the cured body (strength at the completion of the curing) is improved. Ettlingite is a columnar small crystal that crystallizes in the initial stage of cement hardening, and the ettringite disperses and crystallizes inside the cured body after cement hardening, thereby improving the strength of the cured body.

  Therefore, even in the case of a mixture 11 containing a substance that inhibits the setting of cement such as borate, for example, boric acid waste containing borate, setting the film-forming agent 14 causes setting in a short time. The cement solidified body 16 can be manufactured at low cost.

  Moreover, even if it is the mixture 11 containing many borate, the hardened | cured material after the cement hardening by adjusting the compounding quantity of the film formation agent 14 is the thing after the cement hardening of the mixture which does not contain a borate at all. It has approximately the same compressive strength as the cured product. Furthermore, the setting time of the blend 15 can be freely adjusted by adjusting the blending amount of the film forming agent 14.

Furthermore, it is sufficient that the cured product finally obtained by cementing the borate-containing mixture 11 has a compressive strength exceeding the legal standard value for soil storage of radioactive waste (1.5 N / mm ² ). Preferably, it is 3 N / mm ² or more, which is twice the legal reference value, and more preferably 10 N / mm ² or more.

  Further, by using a low alkali type liquid accelerator such as a water-soluble aluminum salt as the film forming agent 14, the handling becomes better compared to the case of using the conventional curing stimulant 112 shown in FIG. Management of the solution is also facilitated. Moreover, since this liquid quick-setting agent is an inexpensive one that is generally used as a spraying agent for tunnels, there is no significant increase in cost associated with the use of the liquid quick-setting agent.

  Next, another embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 3 shows a flow of a cement solidification method according to another preferred embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the member similar to FIG. 1, and description is abbreviate | omitted about these members.

  As shown in FIG. 3, in the cement solidification method according to the present embodiment, first, a flow loss agent 34 is added together with a mixture 11 containing at least borate (or nitrate), cement 12, and water 13. Formulation 35 is formed. It is preferable that the fluidity loss agent 34 is added to the cement 12 at a weight ratio of less than 20 wt%, preferably 1 to 15 wt%.

  Thereafter, in the formulation 35, the initial setting occurs. At this time, as shown in FIG. 4, due to the action of the solvent (solution of fluidity loss agent 34 and water 13) 44 of the mixture 11 containing cement particles 42 and borate ions (or nitrate ions) 43, the compound 35 is Almost no flow.

  Thereafter, the setting proceeds and finally the end of the setting occurs. Thereby, the cement solidified body 36 is obtained. Thereafter, in the cement solid body 36, the hydration reaction of the cement gradually proceeds, and the hardening of the cement solid body 36 gradually proceeds. The cement hydration reaction proceeds for about 4 weeks from the beginning of setting, and after about 4 weeks, the hardening of the cement is completely (or almost completely) and a hardened body (not shown) is obtained. The strength of the cement solid body 36 is an apparent strength, and the strength of the cured body after the completion of the curing is a true strength.

  Here, the addition ratio of the fluidity-reducing agent 34 to the cement 12 is less than 20 wt% in the weight ratio. If it is added more than that, the water 13 and the fluidity-removing agent 34 react excessively and are mixed. The fluidity of the object 35 is completely lost. As a result, the water for reacting with the cement particles 22 is lost, and the cement cannot be set. Examples of the fluidity loss agent 34 include baked gypsum.

  Next, the operation of the present embodiment will be described.

  When baked gypsum is used as the fluidity-reducing agent 34, the hydrated gypsum and water 13 are hydrated and the fluidity of the blend 35 is rapidly lost after the blending and until the start of setting. The hydration rate of this gypsum is faster than the hydration rate of cement. Therefore, as shown in FIG. 4, the cement particles 42 and borate ions (or nitrate ions) 43 in the solvent 44 hardly flow due to the hydration reaction of the gypsum. For this reason, the contact between the cement particles 42 and the borate ions (or nitrate ions) 43 is prevented. As a result, a calcium borate coating (or calcium nitrate coating) is not generated around the cement particles 42, and the hydration reaction of the cement particles 22 is not hindered.

  Therefore, even in the case of a mixture 11 containing a substance that inhibits the setting of cement such as borate, for example, boric acid waste containing borate, by adding the fluidity loss agent 34, it is possible to shorten the time. It can be set and cemented, and the cement solidified body 36 can be manufactured at low cost.

  Even in the case of the mixture 11 containing a large amount of borate, the cement solidified body 36 is almost the same as the cement solidified body of the mixture containing no borate by adjusting the blending amount of the fluidity loss agent 34. Has equivalent compressive strength. Furthermore, the setting time of the compound 35 can be freely adjusted by adjusting the blending amount of the fluidity loss agent 34.

Furthermore, it is sufficient that the cured product finally obtained by cementing the borate-containing mixture 11 has a compressive strength exceeding the legal standard value for soil storage of radioactive waste (1.5 N / mm ² ). Preferably, it is 3 N / mm ² or more, which is twice the legal reference value, and more preferably 10 N / mm ² or more.

  Further, by using baked gypsum as the fluidity loss agent 34, the handling becomes better and the management of the solution becomes easier than in the case of using the conventional curing stimulant 112 shown in FIG. In addition, baked gypsum is an inexpensive one that is widely used in various fields, so there is no significant increase in cost associated with the use of baked gypsum.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

(Sample 1)
Cement and water were mixed to perform cement solidification.

(Sample 2)
A mixture of sodium nitrate (NaNO ₃ ) and sodium tetraborate (Na ₂ B ₄ O ₇ ) mixed at a weight ratio of 2: 1, simulating the residue generated when the volume of actual low-level radioactive waste is reduced. Was made. This mixture was mixed with cement and water to obtain a blend, which was then solidified. The addition ratio of the mixture to the cement was 10 wt% by weight. The water cement ratio (W / C) was 30 to 45%.

For each sample, the setting time (min) and the compressive strength (N / mm ² ) were measured. The setting time was determined by conducting a setting test in accordance with JIS R 5201 and measuring the initial time and the final time of the cement solidified body. The hatched area in FIG. 5 indicates the start time, and the white area indicates the end time. The compressive strength was measured by a compressive strength test in accordance with JIS A 1108, and the compressive strength after 7 days from the start was measured.

As a result, as shown in FIG. 5, Sample 1 started about 100 minutes after the start of compounding and ended after about 300 minutes. Further, as shown in FIG. 6, the compressive strength at 7 days of age was about 22 N / mm ² . On the other hand, as shown in FIG. 5, sample 2 started at about 160 minutes from the start of blending but did not finish until the end. That is, Sample 2 did not solidify. As a result, as shown in FIG. 6, no data on compressive strength was obtained.

  From the above, it was confirmed that the cement itself could not be solidified by using the conventional method even in the case of a blend of 10 wt% in the weight ratio of the mixture with respect to the cement as in Sample 2. .

(Example 1)
Simulates the residue produced when volume reducing actual low-level radioactive waste, and mixes sodium nitrate (NaNO ₃ ) and sodium tetraborate (Na ₂ B ₄ O ₇ ) at a weight ratio of 2: 1. Was made. This mixture was mixed with a water-soluble aluminum salt containing a cement, water, and sulfate (low alkali type liquid quick-setting agent) to obtain a blend, and cement solidification was performed (sample 21). The addition ratio of the mixture to the cement was 50 wt% by weight. Moreover, the addition ratio of the liquid quickening agent with respect to cement was 5 wt% in weight ratio. Furthermore, the water cement ratio (W / C) was 30 to 45%.

(Example 2)
Cement solidification was performed in the same manner as in Example 1 except that the addition ratio of the liquid quick-setting agent to the cement was 10 wt% in terms of weight ratio (Sample 22).

(Example 3)
Cement solidification was carried out in the same manner as in Example 1 except that the addition ratio of the mixture to the cement was 60 wt% by weight and the addition ratio of the liquid accelerator to the cement was 10 wt% (sample) 23).

(Comparative Example 1)
Cement solidification was performed in the same manner as in Example 1 except that a highly alkaline inorganic aluminate compound was used as the liquid accelerator and the addition ratio of the liquid accelerator to the cement was 10 wt% by weight. (Sample 24).

About each sample of Examples 1-3 and the comparative example 1, setting time (min) and compressive strength (N / mm < ² >) were measured. The setting time was determined by conducting a setting test in accordance with JIS R 5201 and measuring the initial time and the final time of the cement solidified body. The hatched area in FIG. 7 indicates the start time, and the white area indicates the end time. The compressive strength was measured by a compressive strength test in accordance with JIS A 1108, and the compressive strength after 7 days from the start was measured.

As a result, as shown in FIG. 7, the sample 21 of Example 1 started about 120 minutes after the start of blending and ended after about 220 minutes. Further, as shown in FIG. 8, the compressive strength at age 7 days was about 9.5 N / mm ² .

In addition, as shown in FIG. 7, the sample 22 of Example 2 started about 20 minutes after the start of blending and ended after about 40 minutes. Further, as shown in FIG. 8, the compressive strength at age 7 days was about 9.5 N / mm ² .

Furthermore, as shown in FIG. 7, the sample 23 of Example 3 started from about 10 minutes after the start of blending and ended after about 20 minutes. Further, as shown in FIG. 8, the compressive strength at 7 days of age was about 18 N / mm ² .

On the other hand, as shown in FIG. 7, the sample 24 of Comparative Example 1 started about 200 minutes after the start of blending and ended after about 380 minutes. However, as shown in FIG. 8, the compressive strength at 7 days of age was about 1 N / mm ² , which was below the legal reference value (1.5 N / mm ² ).

  From the above, each sample of Examples 1 to 3 using the cement solidification method according to the preferred embodiment of the present invention is used even when the addition ratio of the mixture to the cement is a blend of 50 to 60 wt% by weight. Cement solidification was possible. Moreover, each sample of the age of 7 had sufficient compressive strength which exceeded a legal reference value significantly.

  Moreover, when each sample of Example 1, 2 was compared, it turned out that adjustment of a setting time is possible by adjusting the addition ratio of a liquid quick setting agent.

  Moreover, when each sample of Example 2 and 3 was compared, it turned out that adjustment of a setting time and compressive strength is possible by adjusting the addition ratio of a mixture. In particular, it was found that the sample 23 having a higher mixture addition ratio has higher compressive strength than the sample 22 having a lower mixture addition ratio.

It is a figure which shows the flow of the cement solidification method which concerns on suitable one embodiment of this invention. It is a model figure at the time of the condensation of the compound in FIG. It is a figure which shows the flow of the cement solidification method which concerns on other preferable one Embodiment of this invention. It is a model figure at the time of the condensation of the compound in FIG. It is a figure which shows the setting time of the samples 1 and 2 in [Example 1]. It is a figure which shows the compressive strength of the samples 1 and 2 in [Example 1]. It is a figure which shows the condensation time of each sample of Examples 1-3 and Comparative Example 1 in [Example 2]. It is a figure which shows the compressive strength of each sample of Examples 1-3 and Comparative Example 1 in [Example 2]. It is a figure which shows the flow of the cement solidification method of the mixture containing the conventional borate. It is a model figure at the time of condensation of the compound in FIG. It is a figure which shows the flow of the cement solidification method of the mixture containing the conventional borate.

Explanation of symbols

11 Mixture 12 Cement 13 Water 14 Film Forming Agent 15 Formulation 22 Cement Particles 24 Protective Coating

Claims (9)

  A method of solidifying a mixture containing at least borate, boric acid, or nitrate by cement, and adding a film forming agent together with the mixture, cement, and water to form a blend, and cement particles Forming a protective film, which is a compound of a film forming agent and a calcium component, around the cement particles earlier than a compound film of borate, boric acid, or nitrate and a calcium component is formed around A characteristic cement hardening method.   The cement solidification method according to claim 1, wherein the film forming agent is added to the cement at a ratio of less than 20 wt%.   3. The cement solidifying method according to claim 1, wherein the film forming agent is a low alkali type liquid quick setting agent.   4. The cement solidifying method according to claim 3, wherein the low alkali type liquid accelerator is an aqueous solution mainly composed of a water-soluble aluminum salt.   A method of solidifying a mixture containing at least borate, boric acid or nitrate with cement, and adding a fluidity loss agent together with the mixture, cement, and water to form a blend, A cement solidification method characterized by eliminating the fluidity of the above-mentioned composition faster than the formation of a borate, boric acid, or nitrate-calcium compound coating film around particles.   The cement solidification method according to claim 5, wherein the fluidity loss agent is added at a ratio of less than 20 wt% with respect to the cement.   The cement solidification method according to claim 5 or 6, wherein the fluidity-reducing agent is gypsum.   A cement solidified body solidified by using the cement solidifying method according to claim 1. A cement solidified body solidified by using the cement solidifying method according to claim 5.

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